I believe there are a few obscure shovelware titles that the R4 team never bothered to fix......basically games you'd never play anyway. I couldn't say what they were though.

I can't rem what region, but either the (U) or (E) version of FFCC still has the "Thanks For Playing" bug I think. But there's an AR cheat for that, so no one really cares.

Castlevania: Portrait of Ruin tends to lock up on an R4.......there are special ways to attempt to make it work, cut certain sounds, formatting the SD card a certain way....stuff like that. Still basically a problem though.

One of the Tony Hawk games has...some kind of slowdown.....something about a timer issue.....something like that. I don't know for sure, I never played the Tony Hawk games.